Planing boats operating in rough water may experience significant vertical shocks when the boat and wave impact one another. The most powerful shocks occur after a boat has become airborne flying off the crest of a wave, when the boat lands onto a wave face with its keel substantially parallel to the wave surface. Shock impulses on the order of 50 Gs with pulse durations in excess of 40 milliseconds are not uncommon, and such shock is more than enough to cause serious injury. Documented injuries include sprains to the back neck, hip, knee, and shoulder, kidney damage, and broken ribs and limbs.
Typically, naval architects have attempted to reduce this shock by deepening and narrowing the hull, and pointing the bow. These deep-vee hulls impact the water more gradually and with less peak acceleration than shallower, flatter hulls. But deep-vee hulls require deeper water for safe navigation, may have roll stability issues, and generally require more fuel for a given speed than shallow-vee hulls. Moreover, they cannot unquestionably limit the acceleration on the Payload in all cases of boat-water impact.
Boat operators typically attempt to reduce shock by either slowing down considerably in rough water, or slowing down-somewhat while attempting to steer and throttle around the biggest waves while avoiding becoming airborne. The drawback of these approaches is the speed reduction. Military and law-enforcement boats often cannot slow too much without risking mission failure. Offshore power boats cannot slow too much without risking the race.
A number of hardware devices have been developed and are in use, including several that have been patented. All have drawbacks. Perhaps the most serious drawback of previous approaches is that they cannot protect the Payload if the incident shock peak or its rate of rise is too large. Many of these devices work reasonably well provided the peak shock amplitude is fairly low, for example, shock peak under 10 G's with jerk under 100 G's per second. But the performance of these same devices degrades as the rate of rise and/or peak amplitude of the acceleration increases. Faster boat speeds and rougher seas create sharper, more powerful shocks, with peaks on the order of 50 G's and jerk on the order of 1,000 G's per second. Previous approaches are generally based on viscous dampers and springs. A viscous damper's force is a function of the relative velocity of its endpoints. Even if actively controlled, a viscous damper transmits forces to the Payload which depend on the peak load and loading rate of the shock pulse.
A problem related to protection from boat shock is protection from explosive shock. Explosive devices generate accelerations on the order of thousands of G's with jerk on the order of tens of millions of G's per second. Explosions have such short pulse durations, as small as a fraction of a millisecond, that an active protection system would require an extremely high sampling rate, some very rapid processing algorithms to discriminate between noise and an actual explosion, and very rapid actuators to effect protection of the Payload, making an active protection system very expensive, if it could be made at all. Current approaches using passive viscous damping systems would either break or dump fluid out their relief valve under such extreme forces. Traditional approaches to protecting against shock differ somewhat depending upon the nature of the Payload. If the Payload consists of equipment, the traditional approaches have been to either harden it or mount it on resilient mounts. Hardening generally results in increased weight and volume, and often impacts accessibility for maintenance and convective cooling. Resilient mounting often exacts volume penalty in order to accommodate sway and surge of the equipment during shock. In cases where the Payload is personnel, there have also been two similar traditional approaches. The first is to brace for shock, generally involving bending the legs and holding onto handrails while tensing the muscles. The other approach has been some type of resilient interface such as padded seating or heavy sponge rubber deck covering on a ship traversing a suspected minefield. No systematic, engineered approach which can unequivocally protect a Payload from explosive shock has been developed.
Another drawback of many previous approaches is an inability to adjust to the weights of various Payloads. These devices are either overly stiff or overly soft depending upon the Payload mass. Overly stiff devices obviously transmit too much force to the Payload. But overly soft devices may also be inadequate in that they expend all available relative displacement between Payload and vehicle without absorbing all the shock energy. The Payload then bottoms out, spiking the acceleration. Even if the Payload does not bottom out, an overly soft interface takes up more volume than required, impacting its usefulness, particularly in high-performance vehicles.
A further drawback of previous devices is a slow reset time. If the device cannot restore the Payload to its original position before the next shock hits, then the next shock may cause it to bottom out.
The purpose of the present invention is to protect the Payload (personnel and sensitive equipment) from shock. It does so by limiting the force transmitted to the Payload to a low, user-adjustable value, regardless of the peak amplitude or rise rate of the imposed shock on the vehicle or structure.
Another purpose of the present invention is to provide adjustment of the force transmitted to the Payload from the vehicle or structure to accommodate masses of various Payloads without being overly stiff or bottoming out.
Another purpose of the present invention is to have a quick reset time so that it can be fully recovered in time for each subsequent shock events.